One of the most attractive aspects of a storage area network (SAN) is that network connectivity enables a company to efficiently use storage by sharing storage capacity among a number of servers. This may be implemented using a large number of small capacity storage devices. However, unless sufficiently robust management software is employed, such use of small capacity devices in a SAN may result in significant management overhead.
Most users prefer to install large capacity storage device(s) and partition one or more of the device(s), assigning each partition to a different server. For example, existing firmware for enterprise level disk arrays allow users to define multiple redundant array of independent disks (RAID) sets, where each RAID set appears as a different LUN, generally fiber channel (FC) LUNs. Each one of these FC LUNs may be dedicated to a different server. However, to-date special hardware or special backup software has previously been used to implement partitioning in data tape libraries.
An existing hardware-based partitioning scheme for existing data tape libraries is known as shared library services. This implementation requires at least one bridge, sometimes referred to as a quad interface processor, to be placed between the drives and the library controller. The host side of each quad interface processor consists of two SCSI buses, and the quad interface processor may show a single virtual library's controller, with its own SCSI ID, on each SCSI bus. Thus, there may be one virtual library per host SCSI bus, containing the virtual library controller and the drives in that partition. Each partition of such an existing library may have tape storage slots added in increments and drives may be added individually or in pairs. Each internal SCSI bus in this existing partitioning scheme may accommodate up to two drives; drives on the same bus must be in the same partition. Such existing data tape library partitioning systems may use switches to secure partitions. Quad interface processors expose a SCSI target ID for each partition and each SCSI ID can have a separate SCSI/FC bridge attached to it to implement partition security using FC switches.
Existing software-based partitioning solutions typically employ a host system that restricts access to portions of a tape library. The host restrictions are implemented by a mediating (software) process on a host system to enforce partition restrictions. However, this approach is problematic. Specifically, the approach is undesirable if the tape library is utilized in a storage service provider (SSP) environment. In SSP environments, the tape library and the host systems belong to different entities (e.g., the storage service provider and the customers). Placement of software mediating processes on host systems is unattractive, because it increases the burden on the customers to make use of the storage service. Also, corporate environments impose relatively long qualification cycles for new host system software. New software is typically only introduced in such environments once every six to eight months due to qualification cycles. Moreover, many customers are unwilling to allow other parties to place software on their host systems. Additionally, the software mediating process approach is typically incompatible with existing data back-up utilities, i.e., the software mediating process approach requires the use of specialized data back-up applications. Hence, users are effectively denied the ability to run desired backup software.